The present application is based on Japanese Priority Document P2001-145267 filed on May 15, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a drive control circuit suitable for use in a three-phase brushless motor, a motor-driven blower and an electric vacuum cleaner. The electric vacuum cleaner described herein includes various devices which collect various solids or fluids into a collection area by using negative pressure.
2. Discussion of the Background
As a motor, e.g., a motor-driven blower or the like in which the motor is used, there is known one provided with an overcurrent protection function for discriminating an inrush current and an improper current that flow upon startup of the motor-driven blower or the like. As shown in FIG. 11, the inrush current that flows upon startup of the motor-driven blower is high instantaneously but decreases with time. On the other hand, when an overload is continuously imposed on the motor-driven blower or the motor-driven blower is brought into a lock state, an overcurrent continues to flow. Therefore, if an overcurrent detected value Iz and an overcurrent detected value Tz are set and detected simultaneously then the inrush current and the improper current at the startup can be discriminated. Namely, when Tz less than Tb is reached upon Iz less than I, the current is recognized as the improper current and cut off. There have heretofore been known various circuit configurations each having such a function.
This method, however, is accompanied by a problem that although the time is exactly short, a large current flows at the startup and a load is imposed on each electronic part on an electrical circuit. There is therefore known a method of suppressing the inrush current at the startup as low as possible; For example, a method disclosed in Unexamined Patent Publication No. Sho 62(1987)-272877 shows that a PWM inverter device outputs a signal having a short pulse width for a predetermined time alone upon its startup and thereby starts up.
When the motor used in the motor-driven blower or the like is made up of a three-phase brushless motor, systems such as sinusoidal drive, 6-step 120xc2x0 energized drive, 6-step 180xc2x0 drive, etc. have been adopted as a basic system for inverter driving of the three-phase brushless motor. The sinusoidal drive is one ideal drive system, which is driven so that a voltage applied across a terminal of a motor takes a sinusoidal wave. The sinusoidal drive has been used in applications or the like which requires low vibrations and low noise. Also position detecting means high in resolution are required for accurate drive. The 6-step 120xc2x0 energized drive is a system often used as a drive system of a brushless motor, wherein a period in which each motor terminal is in an open state, is given as 60xc2x0, the waveform of a voltage applied across the motor terminal approximates a trapezoidal wave rather than a rectangular wave, and no torque pulsation is low. Since the 6-step 180xc2x0 energized drive does not have the period in which each motor terminal is in the open state, it needs dead band control or the like. The waveform of the voltage applied across the motor terminal is basically determined by switching of an inverter circuit and a DC voltage thereof. These drive systems are used properly according to their uses.
However, these related arts are intended to trigger a pulse having a pulse width less than or equal to the maximum trigger protection pulse width which exists in a non-destructive region of a power transistor, as a control signal. They do not disclose specific means other than the use of the pulse width control.
The basic system of the inverter drive of the three-phase brushless motor conventionally used in the motor-driven blower or the like is suitable for such an application that a load at the startup of a motor-driven blower mounted to an electric vacuum cleaner is extremely small and raised in proportion to the square of a rotational speed thereof, and it needs to reach a high rotational speed in a short period of time as in the motor-driven blower mounted to the electric vacuum cleaner, for example. Further, specific means for reducing an inrush current at its startup has not yet been known.
Accordingly, an object of the present invention is to easily reduce an inrush current flowing at the startup of a three-phase brushless motor upon control of the three-phase brushless motor, particularly to reduce the inrush current at the startup in the form suitable for such an application that a load at the startup is extremely small and it needs to reach a high rotational speed in a short period of time as in a motor-driven blower mounted to an electric vacuum cleaner.
The object of the present invention is achieved by a novel drive control circuit of a three-phase brushless motor, motor-driven blower and electric vacuum cleaner of the present invention.
According to the novel drive control circuit of the three-phase brushless motor, of the present invention, a pulse signal is generated based on a detected signal of rotational position detecting means detecting each rotational position of the three-phase brushless motor to thereby control an inverter circuit which drives the three-phase brushless motor. The drive control circuit or the three-phase brushless motor, of the present invention causes memory to store a first sequence for generating pulse signals for causing currents to flow in armature windings of three phases of the three-phase brushless motor, and a second sequence for generating pulse signals for causing currents to flow in the armature windings of the two phases of the three-phase brushless motor. When the three-phase brushless motor is started up, the drive control circuit generates pulse signals according to the first sequence to control the inverter circuit, thereby reducing an inrush current at the startup, and thereafter performs switching to the second sequence to generate pulse signals, thereby controlling the inverter circuit.
According to the novel motor-driven blower of the present invention, the drive control circuit of the three-phase brushless motor, of the present invention is used.
According to the novel electric vacuum cleaner or the present invention, the motor-driven blower of the present invention is used.